Caution: Adobe's download page may include a checkbox for optional software (such as Google Chrome or McAfee Security Scan) that is selected by default. If you do not clear the checkbox before downloading, that software will be installed on your computer when you open the Flash installer.

Open a Terminal window (in Gnome, click on the Applications menu, select Accessories, and then select Terminal.)

In the Terminal window, change to the directory where you saved the file you downloaded (e.g. cd /home/user/Downloads).

Extract libflashplayer.so from the file you downloaded with the command tar -zxvf install_flash_player_"version"_linux."processor".tar.gz.

As the super user, copy the extracted file, libflashplayer.so, to your Firefox installation directory's plugins sub-directory. For example, if Firefox is installed in /usr/lib/mozilla, use the command sudo cp libflashplayer.so /usr/lib/mozilla/plugins and then enter your super user password when prompted.